<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>三角</title>
</head>
<style>
    .box1 {
        width : 0;
        height: 0;
        /*border: 10px solid skyblue;*/
        border-top: 10px solid red;
        border-right: 10px solid skyblue;
        border-bottom: 10px solid orange;
        border-left: 10px solid green;
    }

    .box2 {
        width: 0;
        height: 0;
        border: 50px solid transparent;
        border-left-color: skyblue;
        margin: 100px auto;
    }

    .jd {
        position: relative;
        width: 120px;
        height: 249px;
        background-color: skyblue;
    }

    .jd span {
        position: absolute;
        right: 15px;
        top: -10px;
        width: 0;
        height: 0;
        /*为了照顾兼容性*/
        line-height: 0;
        font-size: 0;
        border: 5px solid transparent;
        border-bottom-color: skyblue;
    }
</style>
<body>
    <div class="box1"></div>
    <div class="box2"></div>
    <div class="jd">
        <span></span>
    </div>
</body>
</html>